An issue that I've been trying to resolve on 03-06 Silverado's and Sierra's, is where when the ignition is placed in accessory on, the check engine light illuminates, and when started it goes off. However, when cycled back to accessory on, it will not illuminate until the key is left in the off position for about 10 seconds. I have tried swapping out the guage cluster to eliminate that cause, and know a shop that has replaced the PCM, also to no effect. Has anyone else observed or identified the cause of this issue?

Thanks,

 

Do you have any OBD II codes? If you've no scan tool take it to a parts store and have them run the codes.

 

That’s normal. The CEL is directly controlled by the cluster, but the cluster will not turn it on unless there’s a command from the PCM to do so or the cluster is malfunctioning.

The PCM only commands the CEL on during a bulb check (initial key on, whether the key position is ON or ACC) or when a malfunction is present. The PCM doesn’t recognize the key position from ON to ACC as an ignition cycle or a malfunction, therefore it won’t command the CEL on until the the key is cycled off and then on again.